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Dielectric device

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Dielectric device


A dielectric device has a first electrode film having a non-oriented or amorphous structure, a dielectric film provided on the first electrode film and having a preferentially oriented structure, and a second electrode film provided on the dielectric film and having a non-oriented or amorphous structure.
Related Terms: Electrode Amorphous Dielectric Film

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USPTO Applicaton #: #20130320813 - Class: 310360 (USPTO) - 12/05/13 - Class 310 


Inventors: Katsuyuki Kurachi, Hitoshi Sakuma, Yasuhiro Aida, Kazuhiko Maejima, Mayumi Nakajima

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The Patent Description & Claims data below is from USPTO Patent Application 20130320813, Dielectric device.

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric device.

2. Related Background Art

There are conventionally known dielectric devices having a dielectric film and a pair of electrode films laid on both sides of the dielectric film, as disclosed in Patent Literatures 1 to 5. Patent Literature 1: Japanese Patent Application Laid-open No. 2010-103194 Patent Literature 2: Japanese Patent Application Laid-open No. 2009-094449 Patent Literature 3: Japanese Patent Application Laid-open No. 2008-211385 Patent Literature 4: Japanese Patent Application Laid-open No. 2007-277606 Patent Literature 5: Japanese Patent Application Laid-open No. 2006-286911

SUMMARY

OF THE INVENTION

In the case of the conventional dielectric devices, however, it is not easy to enhance the crystallinity of the dielectric and manufacturing cost thereof is also high. The present invention has been accomplished in view of these problems and provides a dielectric device capable of readily achieving improvement in crystallinity of the dielectric and lower cost.

A dielectric device according to the present invention comprises: a first electrode film having a non-oriented or amorphous structure; a dielectric film provided on the first electrode film and having a preferentially oriented structure; and a second electrode film provided on the dielectric film and having a non-oriented or amorphous structure.

In the present invention the “preferentially oriented structure” refers to a structure such that in the result of X-ray diffraction measurement, an intensity of a peak ascribed to a certain crystal lattice plane is not less than 50% of a total of intensities of all peaks. The “non-oriented structure” refers to a structure such that in X-ray diffraction measurement, an intensity of a peak ascribed to any crystal plane is less than 50% of a total of intensities of all peaks. The “amorphous structure” refers to a structure such that in X-ray diffraction measurement, no peak is observed to be ascribed to a crystal lattice plane.

In the present invention, the dielectric film is preferably (001), (101), or (110) preferentially oriented.

In the present invention the two electrode films can be composed of an elemental metal or can also be composed of an alloy containing two or more metals, and they may contain an element other than metals, without inhibiting the characteristics including electrical conductivity. The two electrode films can have their respective compositions different from each other, but they preferably have the same composition.

In the present invention the dielectric may be a piezoelectric material or may be a paraelectric, pyroelectric, or ferroelectric material. Among others, the piezoelectric material is preferable.

In the present invention, an oxidation-reduction potential of every metal element forming the first and second electrode films is preferably higher than that of every metal element forming the dielectric film. This makes the dielectric film chemically and electrically stable, without being reduced by the electrode films, thereby to further improve the lifetime and reliability of the dielectric device.

The first and second electrode films are preferably composed of a metal selected from Al, Ti, Zr, Ta, Cr, Co, and Ni or composed of an alloy containing metals selected therefrom. Particularly, in cases where the dielectric device has the dielectric film composed of only a metal element or metal elements having a sufficiently low oxidation-reduction potential, when the constituent elements of the two electrode films are selected from the aforementioned metal elements, interfaces between the electrode films and the dielectric film become chemically and electrically stable, thereby to further improve the lifetime and reliability of the dielectric device.

One principal surface of the dielectric film can be in contact with the first electrode film and the other principal surface of the dielectric film can be in contact with the second electrode film.

In the present invention, the dielectric device preferably further comprises an intermediate film composed of a metal selected from Al, Ti, Zr, Ta, Cr, Co, and Ni, between at least one electrode film and the dielectric film, for the purpose of improvement in adhesion between the two films. An oxidation-reduction potential of the metal forming this intermediate film is preferably lower than that of any one of metal elements forming the dielectric film.

The intermediate film can be in contact with the electrode film and the dielectric film.

It is believed that a requisite minimum oxidation-reduction reaction occurs between the intermediate film and the dielectric film, so as to improve adhesion between the films. However, if the oxidation-reduction reaction is promoted too much, a composition balance of the dielectric film will be lost, so as to cause degradation of the piezoelectric property and other properties in some cases; therefore, there is, naturally, an upper limit to the film thickness of the intermediate film.

When the dielectric device comprises the intermediate film, an electroconductive oxide film composed of an electroconductive oxide may be provided between the electrode film and the dielectric film, preferably between the intermediate film and the dielectric film, for the purpose of preventing characteristic degradation of this device. This configuration makes the dielectric film less likely to be reduced by the electrode film, thereby to further improve the device in degradation of characteristics.

The intermediate film or the electroconductive oxide film can be in contact with the dielectric film.

The dielectric device can further comprise a metal film having a preferentially oriented structure, between the second electrode film and the dielectric film, and the metal film can be in contact with the second electrode film and the dielectric film.

According to the present invention, the crystallinity of the dielectric film in the dielectric device can be readily improved and it becomes feasible to achieve replacement of materials of the two electrode films with inexpensive materials and increase in throughput of deposition process.

BRIEF DESCRIPTION OF THE DRAWINGS

Sections (a) to (d) in FIG. 1 are schematic sectional views of dielectric devices according to embodiments of the present invention.

FIG. 2 is a table showing oxidation-reduction potentials of metals.

Sections (a) to (g) in FIG. 3 are schematic sectional views showing methods for manufacturing the dielectric devices in FIG. 1.

FIG. 4 is a schematic sectional view of a dielectric device in Comparative Example 1.

FIG. 5 is a drawing showing a relation of thickness of underlying Pt film versus degree of orientation of dielectric film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Dielectric Device 100A)

A dielectric device 100A according to an embodiment of the present invention will be described with reference to (a) in FIG. 1. The dielectric device 100A is disposed on a resin layer 7 which is laid on a support substrate 5, and has a first electrode film 4, a dielectric film 3, a metal film 2, and a second electrode film 8 in the order named.

(Dielectric Film 3)

The dielectric film 3 has a preferentially oriented structure. The “preferentially oriented structure” refers to a structure such that in the result of X-ray diffraction measurement, an intensity of a peak ascribed to a certain crystal lattice plane is not less than 50% of a total of intensities of all peaks. The dielectric film 3 is preferably one such that in the result of X-ray diffraction measurement, an intensity of a peak ascribed to a certain crystal lattice plane is not less than 80% of a total of intensities of all peaks.

The dielectric film 3 is preferably (001), (101), or (110) preferentially oriented. This configuration allows the dielectric film 3 to be a dielectric body with excellent characteristics.

When a piezoelectric film is used as the dielectric film 3, examples of piezoelectric film preferably applicable include films of KNN or equivalently (K,Na)NbO3, LN or equivalently LiNbO3, AlN, and so on. Other applicable materials for the dielectric film 3 include MgO, STO or equivalently SrTiO3, BTO or equivalently BaTiO3, and so on.

There are no particular restrictions on the thickness of the dielectric film 3, but the thickness is normally in the range of about 1000 nm to 4000 nm.

(Electrode Films 4, 8)

The first electrode film 4 is laid on a bottom surface of the dielectric film 3, while the second electrode film 8 is laid on a top surface of the dielectric film 3. Each of the first electrode film 4 and the second electrode film 8 has a non-oriented or amorphous structure. Both of the two electrode films may have the amorphous structure; or, both of the electrode films may have the non-oriented structure; or, one electrode film may have the non-oriented structure while the other electrode film has the amorphous structure.

The “non-oriented structure” refers to a structure such that in X-ray diffraction measurement, an intensity of a peak ascribed to any crystal plane is less than 50% of a total of intensities of all peaks. The electrode films 4, 8 are preferably those such that an intensity of a peak ascribed to a certain crystal lattice plane is not more than 10% of a total of intensities of all peaks. The “amorphous structure” refers to a structure such that in X-ray diffraction measurement no peak is observed to be attributed to a crystal lattice plane.

The electrode films 4, 8 are composed of a metal element or metal elements and there are no particular restrictions on the metal element or metal elements, which can be selected from a wide variety of elemental metals and alloys.

In terms of improvement in reliability to prevent degradation of characteristics due to the battery effect, however, an oxidation-reduction potential of every metal forming the electrode films 4, 8 is preferably higher than that of every metal element forming the dielectric film 3. When this condition is met, an oxidation-reduction reaction is remarkably suppressed between the dielectric film 3 and the electrode films 4, 8 to reduce time degradation of the dielectric film 3 due to the battery effect, so as to enhance the reliability of the device. The material of each of the electrode films 4, 8 preferably has a melting point sufficiently higher than heat loads applied in subsequent processes.

For example, when the dielectric film 3 is composed of barium titanate, the electrode films 4, 8 to be employed are preferably films composed of a metal selected from Zr, Ta, Cr, Fe, Co, Ni, and Cu having the oxidation-reduction potentials higher than that of Ti (oxidation-reduction potential: −1.63 V or higher), or films composed of any one of alloys of these metals.

For example, when the dielectric film 3 is composed of potassium sodium niobate (KNN), the electrode films 4, 8 to be employed are preferably films composed of a metal selected from Ta, Cr, Fe, Co, Ni, and Cu having the oxidation-reduction potentials higher than that of Nb (oxidation-reduction potential: −1.099 V), or films composed of any one of alloys of these metals.



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stats Patent Info
Application #
US 20130320813 A1
Publish Date
12/05/2013
Document #
13487530
File Date
06/04/2012
USPTO Class
310360
Other USPTO Classes
310363, 310365
International Class
/
Drawings
6


Electrode
Amorphous
Dielectric Film


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